Critical Path Slowing Down Performance?

We have recently upgrade to Primavera 15.1.  We saw improved system performance compared to our older version (6.2).  However, we have recently begun a major, time-critical project and it seems like every time we make a major change to the critical path line it takes 10-15 minutes to schedule.  Is this a known issue (changes to critical path taking longer/slowing down performance)?

Thanks

Angela