Initial Biztalk call takes more time then subsequent calls

Once we deploy a solution to BizTalk, the initial call to it takes more time (approx 1-5 mins or more at random) then the following subsequent calls. Also if there haven’t been any calls for some period of time say half an hour or one hour (not sure) , it’ll again take longer period of time for the first call after that idle period.

As we’ve studied this is because, once a call is made for a specific BizTalk assembly, it is loaded into the memory, hence the call takes longer to fulfill for the first time, but from then onwards it performs faster because the assembly being already in the memory. But this behavior is not desirable in most cases as you need a prompt or consistent response time all the time.

Is there any solution to this problem, so that initial calls made to the BizTalk project are faster as well, as are the subsequent calls? Also is the time BizTalk retains that assembly in the memory configurable, if yes then how?