Are they all going to played at once?
I turned on six that are on a single 15A breaker. Three 90's, three +2010 pins, and two active subs (not doing anything). All LED'ed. Power draw was 800W according to Smartthings and a current sense on the pinball breaker in the fuse box. We usually do this every weekend but only play one pin at a time with the subs cranking with never an issue. But when company is over, two might be played at a time. Apologies...a little bit of a geeky comment: That wasn't what they refer to as 'VA' (apparent power), which is used when the current and voltage aren't entirely in phase - it was just 120V x current, so the numbers are a little misleading
If you are really interested, I can plot by using Initial States that monitors the pins real time (i.e. current vs. time). Pins are rather sporadic - meaning they don't draw a lot of current all the time. It really varies with coils firing which are short term events.
EM's are a different beast. I think the last EM I owned drew 500W (with LED's) just sitting there.
Any chance your smart plugs report current or wattage? Many are able to do that.
Sorry - I know your question was about the smart plug at 10A and my six pins are plugged into three outlets - hope this helps a bit tho. If interested, I can just run three pins on a single outlet if interested. When I did this, I was more worried about tripping the 15A breaker.
But as others mentioned - you might be loading the smart plug a bit and would likely grab some more, or find some rated for 15A. Not sure how much I trust the Chinese smart plugs and their ratings.