Count number of occurrences in file. conditional pattern matching

Sorry if the title doesn't make it clear.

I have a file to be read every 15 mins and find a particular pattern in it (e.g. timeout). File does not have any fixed update frequency.

Outcome expected:- 1. if pattern is found 3 times in 15 mins, run command1. 2. if pattern is found 5 times in 15 mins, run command2.

File to be read from last read position for each check.

Thanks, GRV