15 seconds is not enough per move. If you really feel like the timer has to be shortened make it at least 30 seconds. As for the overall timer 5 minutes also feels not enough at all.
Also I never encountered a person timestalling me in all my playtime. Dont know if I am just lucky but I dont feel like timestall is a problem.
Pokemon is very strategic, so not having enough time to think about your next move would feel very bad in a game like this.
You have to think what move you want to use, what move your opp will use, predict, switch, thinking about the risk/reward of the move your doing, considering if its okay to let the pokemon die or you still need it in the battle, etc.