Oh and one more thing, if you haven't got the skis mounted yet, remember to make sure the tech mounts them on the front end of the adjustment range so you can get the most time out of the mount.
*Take this following statement with a grain of salt, the difference between rental boots and fitted ones is immense, Put please take the time to read all of it*
I will probably get a lot of hate for this, but to tell the truth, I have been on the season rental train for all of my skiing seasons for as long as I can remember. For the same reason as you, I kept growing and growing. I am now 16 and my feet have finally stopped growing and I am 100 percent with no regrets getting off of the rental train. I have ridden the same exact boots two seasons ago and very similar boots last season (same manufacturer, flex, different shell i think).
Don't let yourself tell yourself that you cant do something just because your boots were made for cruising groomers with the family. That mindset is not the positive mindset that I always had to keep me happy when skiing. Don't focus on you'r equipment. I was really fucking stupid and I would tell myself I was a bad skier because of my equipment. I got better when I was happy.
The boots held up pretty well to my standards for what I was doing, and probably more than what they were supposed to so. Being rental boots they are built to be pretty burly but comfortable. I have skied the steepest "Big mountain" stuff in Summit county (Breck, Keystone, A Basin) with solid speed and almost complete control. I rarely felt held back in them, except for when I am going fast in big mogul runs and there is just too much room in them (because rentals have to be wide) to have good control. At that point when they start to get bad, they get really bad, I took some very bad falls because of not having a connection to my skis from my boots.
I was gifted with very neutral, generic feet, so the boots performed somewhat well for my feet which brings me to my next point. Your feet are not my feet. You could have a totally different experience with these boots than me. That is the importance of well fitting boots. The very second that your feet stop growing, start looking into getting boots fitted
Sorry if that was suuuper rambly, but I hope I helped and made sense.