There are such machines as a powered floor scraper. I rented one years ago to remove the old adhesive during a 100% glue-down vinyl floor replacement. Still wasn't a quick job, but at least I wasn't on my hands and knees.

Do not use an adhesive remover. Any residue like that will cause issues with vinyl. Vinyl is an active chemical even in the solid state. It LOVES to stain when it comes in contact with stuff like old adhesive or adhesive remover.

I take it the sunroom is fully heated/cooled enough for vinyl? Vinyl does not like direct sunlight. If any part of the sunroom gets POOLS of sunlight sitting on it, the vinyl is going to have an issue (vinyl LOVES to warp...and discolour...sometimes it turns purple).

Just for sheeps and giggles, go ahead and place an indoor-outdoor thermometer on the sunroom floor where the sun pools during the day. If the thermometer rises ABOVE 85F, you know you will have MASSIVE issues with 99% of all vinyl floors.

As for the adhesive removal, sanding is your best option. Remember to purchase twice as many pads as you think you'll need. The adhesive loves to GUM UP the pads. They need to be replaced frequently.

Thank you both for the great advice. much appreciated! I will also be using the indoor/outdoor thermometer to gauge the temperature. these are things I would never think of!