How much weight loss is reasonable and sustainable per month

Do you weigh at the same time each day? It's possible that some of that loss on the scale is timing. It is longer from the time you eat supper until the morning when you weigh, so your body has time to digest more food and release more waste.
Yes, I would be impatient to lose a little faster.

If you lost 1.5 kilos and you're happy with your routine, that's perfect IMO.

There are a couple of general rules of thumb that are often suggested here, concerning weight loss rate.

One is to lose no more than about 0.5-1% of current weight per week, with bias toward the lower end of that unless severely obese and under close medical supervision for deficiencies or complications. So, for you that would be just under half a kilo to one kilo per week, preferably half a kilo.

It's fine to lose slower, especially if that makes the process easier to stick with long enough to lose a meaningful total amount of weight.

An alternate rule of thumb is to cut no more than about 20%-25% from current-weight maintenance calories, which usually will be a similar number. This one doesn't seem to be applicable for you, since it sounds like you're not calorie counting. (It's not essential to calorie count; other methods like what you're doing are fine, as long as they're working for you.)

Too many people start with a goal of very fast loss . . . I guess wanting to get it over with and go back to normal? That's usually more of a path to yo-yo weight than a path to long-term healthy-weight maintenance, it seems like. IMO, maintaining a healthy weight long term is the true prize in this situation.

Gradual loss, alongside learning new sustainable habits, is perfect. A sensibly moderate weight loss rate we can live with, and the practice of new eating/activity habits during that, can get a person to goal weight (and keep them there) in less calendar time than some extreme, restrictive difficult regimen that causes deprivation-triggered over-eating bouts, breaks in the action, or even giving up altogether.

Sounds like you're doing great!

On average losing 1-2 lbs per week is reasonable and possible. The less you have to lose the longer it takes.
So, 3.3 lbs in a month seems reasonable to me.
Slow and steady.

There is a sense in which each round of weight loss can become more difficult, especially if we lose fast.

I'm oversimplifying for brevity, but a common pattern I've seen in my social group is losing weight fast by going to ultra low calories, eating mostly veggies/salads, doing a bunch of cardio . . . until it becomes unrealistic or unsustainable, and the person gives up. They "go back to normal", which involves eating more treat foods (fried foods, baked goods, candy, etc.), and not doing much if any exercise.

The loss phase doesn't include adequate calories, adequate protein, or strength challenge to remind the body we want to keep muscle, so unnecessarily much lean tissue is lost alongside fat loss. The regain phase still doesn't have enough protein or strength-challenging activity, so the regained weight is almost entirely fat.

Repeat that process, and the result is gradually worse body composition: Higher percentage of fat at any given weight, lower percentage of muscle.

That lowers metabolism a little bit, because a pound of muscle burns more calories even at rest than a pound of fat. But that effect is pretty small: Researchers estimate maybe 2-8 or so calories more per day per pound of muscle vs. pound of fat. (That would be roughly 1 to 4 calories per kg of muscle vs. fat daily - tiny effect.)

The bigger deal is that worse body composition makes it harder and less fun to move, not just exercise, but also daily life movement. Through that mechanism, we're gradually (and perhaps unnoticed) moving less, burning fewer calories. Research suggests that even fidgeting can make low hundreds of calories difference daily between fidgety people and otherwise similar non-fidgety ones. I'm not suggesting people fidget for weight loss, just saying that reduced movement can happen almost invisibly. I don't notice how much I fidget; do you?

If you're losing slowly, I think you're on a better course. That, plus getting enough protein (ideally in the context of overall good nutrition) and some strength-challenging exercise can help avoid another negative hit on body composition, maybe even reverse the issue if a person sticks with it long term (even at goal).

Also, it's possible to intentionally increase daily life movement. Various MFP-ers share their ideas about that here:

http://community.myfitnesspal.com/en/discussion/10610953/neat-improvement-strategies-to-improve-weight-loss/p1

If exercising, I'd encourage sticking with a manageably challenging routine, not some extreme exhausting thing. Over-exercise can cause fatigue, and also reduce daily life movement (subtly or dramatically), simply because we rest more. That's counter-productive for weight loss, plus over-exercise isn't even the best route to fitness improvement. If fitness improvement is a goal, slow and steady works there, too. As we get fitter, we can increase exercise duration, intensity or frequency to keep that manageable challenge always present (or change exercise type). That ongoing challenge is what creates fitness progress.

You're doing great. Hang in there. Weight loss is a good goal, but IMO staying at a healthy weight long term, ideally permanently, is the really big prize, like I said in my PP on this thread. That depends on developing sustainable new habits we can continue forever, which is kind of the antithesis of the "lose weight fast" mentality.

Just my opinions, though . . . from around year 8 of maintenance, after a year of loss (obese to healthy weight) that followed around 30 previous years of overweight/obesity.

Best wishes!