You are getting more count of trades on M15 probably because you have more data on it ( I guess you have the max for EA Stduo 200k there?).
So basically the more bars we have the more count of trades we can expect to see. Of course it depends how you set the generator/reactor, acceptance criteria, etc.
Just be careful if you use small count of trades and higher win/loss ratio, not to go in over-optimized strategies. Make sure that you do the Monte Carlo test and Demo testing (I know that you do demo).