Resource Usage of Prestashop 1.5?

[CrystalPhoenix18]

Three weeks ago I upgraded to Prestashop 1.5.6.  I bought a new theme, Alysum by Promokit.  I laboriously uploaded all my old products via CSV.  It all seemed to work fine BUT suddenly I had serious spikes in resource usage that I had not had before the upgrade.  Kept crashing the server on shared hosting, so as my provider's insistence upgraded to VPS, but I've had nothing but problems. I have APC cache installed & running, but I still seem to keep running high stats.  Back office shows 400 to 600 visits/day - so not excessive.  I've put in a robots.txt.

Does anyone know if PS 1.5 is a lot more resource hungry than 1.4?  Could it be my theme?  Any thoughts on how I can reduce this?  I haven't had any orders off the website for 3 months so can't really afford to go dedicated or even upgrade to next level of VPS.

any help would be appreciated.

http://thestitchersmuse.com