I'm not really suggesting you spend hundreds and hundreds of hours, but 15 hours seems way too little if you want to compete on any level. Even if you want to make small short games, and clones, I still think it's good to invest a bit in some nice unique art style, or some unique feature for example to stand out of the crowd a bit, and at least polish it, to make if feel polished and professional.
And also. If you spend 15 hours developing, i would suggest spending just as much or even more in marketing. Contact reviewers, youtubers, etc etc, to get some feedback and exposure. If no-one even knows the game exists it's hard to get downloads. If you only rely on people stumbling across the game in an app store, you should probably spend another 15 hours, tweaking description, screenshots, etc optimizing your chances of people finding the game, and wanting to download it.
I'm just saying that 15 hours development time and then just uploading somewhere hoping for the best, seems wayyyy tooo little, for any decent quality production at all.
Multilply those 15 hours a bit.
15 hours developing
15 hours artwork and animations
15 hours testing and feedback, bug fixes and polish.
15 hours marketing, description, video trailer...
Take pride in your work, make something to the best of your ability and that looks fun and is fun to play. Even if it's short, small games. The effort will shine through.