First off if you can bunny hop 15'' thats better than most. If you do trail riding then that height is more than fine, But if you want to get higher I know how. I can hop atleast 2.5' cleanly and hop onto larger objects like loading docks with use of a bashguard (i ride a 35ish pound bike too). If you hit a flat spot on your improving your hop you are probably using the one stage hop or heave the bike up style.
This is basically how I do a bunny hop but to really learn it you should probably go watch trial videos on the internet.
First I roll at a fast jog pace towards whatever I am jumping. Generally the slower I go the higher I jump. So if I’m jumping my max of around 2.5 feet I’m rolling at about a fast walk (maybe a tad faster). If I’m jumping less than that I go faster because I can. It’s a comfort thing you just got to feel out for yourself.
Right before the jump I make sure my pedals are in the proper position. My strong foot forward (I don’t even think about this it just happens… I don’t even know which foot is my strong one). Then as I’m a foot to 3 feet away I will pull up on the handle bars into a wheelie (the distance before the jump depends on how fast you are moving). Its good practice to try to get your front wheel as high or higher than what you are jumping on the wheelie stage.
Second step is going to be a little vague. It’s hard to explain what to do because I’m not quite sure of how I am doing it, but you will know when it happens. As I am in a wheelie I push on my pedals extremely hard (your rear tire should smush like you hit a bump or something), and then it’s a leap that consists of using your legs to lift the rear of the bike up along with a little of your arms. You might ask how do you lift the rear end up using platform pedals. The answer is: not easy…. you kind of scope them up by applying pressure with your feet backward.
If all goes well you are now in the air, and you should try landing on your rear tire or at least flat on both tires. If you are hitting nose first you are doing too much rear hop and not enough wheelie. I learned this type of hop in two stages and I think it’s the quickest way to learn. First practice wheelies. Not too high at first just get your front end up like 6 or 8 inches. Do this until doing a wheelie is second nature. Then try coasting at a slow pace and hopping your rear tire off of the ground. Not high again just around 6 inches. Remember to apply backpressure with your feet and pull up too. Do this a lot since its not something you do on a bike regularly. Now put those two motions together. The trick is to get a very smooth transition between the front hop and rear hop to gain max height. Think skateboard Ollie. Front wheels go up first on a skateboard (like doing a wheelie), foot drags up along the grip tape on the deck of skateboard (like applying back pressure and using a little arm strength), and rear end comes up.
For me my legs get tired first when practicing, yours should probably too. If they do that means you are probably doing the hop correctly. Its going to be a rough learning experience since you’ll most likely be “out of time” and clank your front wheel down hard a lot. What I like to jump over is stacked up 2X4’s so if you hit them they fall over. If you find yourself consistently hitting nose end first. Find a table top like structure to jump on that and land evenly on the top of that structure. Good luck its going to take a lot of practice to get good at this. Have a buddy watch you so he can explain to you what you are doing (that will speed up the learning process).
