Should I Even Bother?

So, I just got offered an amazing free lease from one of my friends on her VERY green horse. I would say he's about 15 hands, no more than about 15.2. He's a thickly built paint horse, built pretty level, nothing too uphill.
He just turned 7 years old, super green. He's got a great walk/trot, very adjustable, and will frame up nicely when asked. He doesn't quite understand canter yet though. He'll pick up his right lead with encouragement but he doesn't understand fully that I can be on his back while he does so. He doesn't really get the left lead yet. He will do a leg-yield and a tiny bit of side-pass if asked but I don't neccessarily know if he looks great doing it. But he's making progress fast. He's willing and a fast learner.
I'm an experienced rider, I have about 6 years of hunters, jumpers, a little eventing, and basics of dressage. I do plan on getting a dressage instructor in the next month or so, also.
But should I bother with dressage? Would it be worth my time? Do you ever think we could go above training or first level? He's a huge project, I know. But would it be worth my time?
I'll try to get pics and/or videos soon!

I think it would be worth it but it depends how far he is with cantering. But you could always start him with walk and trot to get him used to the atmosphere.

It depends on what you want to gain out of it, almost any horse can reach an acceptable level of dressage with correct training and fitness.

However as he is a green horse you will have to take the good with the bad, it may/most likely will take a while for him to be ready for competition, if you're willing to put in the time and effort for him then do it, if not.. Leave it be.

If yuo do decide to lease him, make sure you have a very well put together lease contract. It is useful to write one up and go to a lawyer to have them firm it up and clarify it so there are no holes.
Personally, I wouldn't expect the horse to go past training level at a competitive level. From a training perspective, the horse could be performing movements from PSG if he is talented enough, but he will probably never be able to put a test together well enough to be competitive.
To put this in perspective, I owned a quarter horse, in training level at our best we could score 65%, in first level at our best, we had trouble breaking 60%. At his peak he was schooling half pass, shoulder in, travers, changes, and starting pirouettes. Even though he was schooling these movements and doing them quite well, in a competitive test setting he would not have scored above 55% past first level because he never had a medium or extended trot and his collected work was difficult for him conformationally. Keep in mind that these days in dressage to be competitive at any level you need to be consistently scoring in the high 60's and low 70's.
I would be wary about how sound he is, a 7 year old horse should be able to canter. Before taking any further steps, I would ask for a complete veterinary exam.

Good luck!

Thanks guys! I appreciate it!
As for his age, he was started at about 3, but his owners were really rough with him and really messed him up. They then threw him out to pasture for a few years, when my friend got him at about 5 years old. She had started doing w/t/c work on him and had jumped some cross rails, but she got terribly ill with mono and has had immune problems since so he hasn't been really ridden in about a year or so.
I'm willing to work though(: I'm used to greenies.
I appreciate everything! Hopefully we can beat the odds and one day make it to Training level!