15 inches of vac at idle

Do you have a lot of miles on the engine?
Actually pretty good vacuum for cam.
There are some cylinders a little low,if its an old build/lot of miles a de-carb would help.
Do it when next oil change is due though.
As you will want to change the oil after the de-carb is done.
I prefer to warm engine up and pull all the plugs and buy a gallon of pb rust blaster,about 4-5 ounces per hole and let it sit overnight.
Bump it over the next day before reinstalling the plugs just incase it didn't all leak by the rings.
Put plugs in and make some serious smoke,about 1700 rpm until it quotes smoking,change the oil and filter.
Good to go,bet you will feel the difference.