Need some ideas to build a pantry spice rack on wheels...

Have you looked 2nd hand/consignment/"antique" stores for a small bureau, console or cabinet that you could use as a frame? If you live near an architectural salvage kind of place, where they remove cabinets, doors, hardware and built-ins from old buildings before they are torn down, it's a great way to find solid wood, quality pieces that might just need a backing or stripping. It would save you a LOT of work than starting from scratch and you could preserve the original 'flavor' of the piece as well as getting some extra-ordinary details that will make your piece unique and maybe even a family heirloom... Since you work with wood,I'm guessing you'd want a solid wood piece of furniture to start with. I have seen some amazing piece made from dressers that have the drawers removed and replaced by shelving...I'm intrigued by your description of it having wheels - is this planned for a countertop, or as a freestanding unit?

Is 15 ft really inches?

Maybe you could work with a design similar to this one- https://www.hometalk.com/diy/organize/kitchen/diy-spice-rack-on-wheels-29051620

I've got a pantry with adjustable shelves that are 15" deep. I'm assuming that's why you have your depth limit. You have a bottom shelf 22 " high and a space 13" wide to put this unit in. It's rolling and short, requiring you to bend over to access. Drawers will give you a view of caps, which you could label. Put shelves at variable heights to maximize the short and taller spices. I'd consider surrounding 3 or less sides with single deep shelves to hold some oddball sized stuff. leaving them "open" for access with a slat to provide something to hold the things on the shelf. As another thought, you might be able to find turn tables which you could use instead of or in combo with the baskets. Sounds like a "fun" creative project. Years ago, I made something similar to Soshana's thought. Attached slider/guides on the back to keep it upright and stabilized with a cord attached to the wall and unit to prevent it from being pulled out all the way by accident. I had a bigger gap to work with. I designed a pantry in this house. My mom always told me, "you have to absolutely 3 things in the house" a pantry, mudroom and back toilet with sink. One more idea for you. We had several cooking utensils taking up space in the kitchen drawers. We all have them. Multiples of the go to ones and the use seldom ones. Any way, I had a wall in the pantry that I put up some pegboard on and put those things there. Easily findable and didn't get in the way. Good luck.