My son also was able to climb out of his crib at 15 months. We just moved him to a twin bed and put up the side rail for about 2 months. He adapted just fine. It took a few days of him testing the waters and coming out of bed a bunch of times at nap and bedtime. I also put a sleeping bag on the floor just in case he somehow rolled off the bed at night (which he did a few times even with the bed rail on, but never got hurt, just fell asleep on the sleeping bag).
We did think about the crib tent for a bit at first. But then we figured if he was strong and smart enough to climb out of his crib and land safely on the ground, he would figure out how to either break or get out of the crib tent just as fast. After all it's only made of mesh on the top. But that's just us.