SP taking 15 minutes, but the same query when executed returns results in 1-2 minutes

Question

So basically I have this relatively long stored procedure. The basic execution flow is that it SELECTS INTO some data into temp tables declared with he #

Answer 1

Try recompiling the sproc to ditch any stored query plan

exec sp_recompile 'YourSproc'

Then run your sproc taking care to use sensible paramters.

Also compare the actual execution plans between the two methods of executing the query.

It might also be worth recomputing any statistics.