Tips for my first 15k

Do you have a training plan? If you don't check out Hal Higdon's Half-marathon plans, longer than your race so you can skip the longest runs if you like (or be ultra-prepared for the race and have a really enjoyable experience)

It's a very individual thing. If your diet is adequate and you train progressively leading up to the race you may find you don't need any nutrition during the race (most adults can store enough glycogen to get you through 90 minutes) If you do find yourself feeling fatigued during your longest runs a gel isn't going to hurt......just make sure you train with whatever you're going to race with (and try your first gels in close proximity to home or washroom facilities - I've never experienced any gastrointestinal problems but some people do and you don't want any surprises on race day)

Similarly hydration for your race takes place in the days leading up to it not on race day itself. Personally I'd stick to water, you shouldn't need to replace electrolytes in that distance but if you decide to use a sports drink the advice is the the same as for gels.....train with whatever you're going to race with. You don't want to drink too much while running, water sloshing around in your stomach can cause cramps - think small sips. Typically during my training runs I don't even carry water unless it's going to be 90 minutes or more and it's hot.