A lot of phones of that type nokia got lag that can be if your memory card is full or the phone is just old i got one friend that got almost the same nokia and he got really big lag but that is coz the phone is old if u want delete most of the things form your phone and keep only the music etc... that you need
Try updating your firmware version, I had the same problem too but it was on videos. While playing videos it was laggy so I updated my firmware. Search it on google