You have the version with the more elaborate decor on the face plate and the round plate in the back? I hope to find one too : -) The later ones are sort of pin striped. It's a lucky find, yours are in nice conditon too. My 201 has the striped plates.
Like mentioned, 3-1 oil are know to turn machines sticky and sluggish, particularly if left to fend for the selves for a while. I have cleaned machines up with spray can oil, then turn to Triflow or Finish Line Ceramic, added teflon can make a difference sometimes. They use vaseline for the grease wick, since modern syntetic greases are solid and doesn't behave the way it should. Some use teflon grease for the worm gear and parts behind the hand wheel, but for the motor bearings, something else is needed. It's hard to find the saponified grease Singer used to sell in small tubes.
Best of luck with your new machine, model 15 is many peoples favorotie :- )