You may be able to upgrade the RAM memory capacity to help OS X 10.10.x
run better in the old MacBook Pro. Depending on what model version you have
the amount of total supported RAM may vary. More recent reputable resellers
of quality guaranteed RAM have found several models of Mac can use more
capacity than originally indicated.
Had you supplied exact model information, this space could have directed you
to more details on that aspect. You can correctly identify your MacBook Pro
and look into upgrading the RAM from OWC macsales.com or Crucial.com to
get the better guaranteed product. I've never bought from them but they are
recommended and have good products, esp at OWC online.
•How to identify MacBook Pro models - Apple Support
•MacBook Pro: How to remove or install memory - Apple Support
For detailed information on all Apple mac products, you could check spec info
at http://everymac.com & also consider the download app http://mactracker.ca
In any event...
Good luck & happy computing! 🙂