J.P.
We have 4 kid and have bought our share of...well, everything, before we end up knowing what works for us.
We bought the AeroBed Sleep Tight Inflatable Bed for Kids. My first son didn't sleep well on it, but the rest have. It's heavy and bulky, AND so loud when they move around at night. It's 12 pounds.
We then bought the Regalo My Cot Portable Bed Royal Blue and it's easy up and down, packs nicely and doesn't take up a top of space. It's weight is 7 pounds, which the Pack N Play is 20 pounds.
Depending on your child and his size, the KidCo PeaPod with Self-Inflating Mattress might be your best bet. The reviews show without the mattress that the ground gets very hard. It's weight is 4.5 pounds. It would seem a bit claustrophobic for a 15 month old, but perhaps not. Buy it early and find out, so you have time to change your mind, if necessary.
Have fun!