Mounting computer to a particle board

I don't think it would be an issue. Just make sure to pre drill holes the correct size and use screws with a coarse thread. Make sure the screws don't penetrate the other side as well.

I mounted a computer on the side of a similar desk with multiple Command™ strips once. It was fine structurally.

Are you certain the entire surface is solid? I've got an IKEA desktop, and it's got solid wood around the edges, but the center is a hollow-core/cardboard honeycomb type of construction. The wood in mine (probably particle board) extends in about 2" (~5cm) but then the rest is that hollow-core construction. Tapping on the desktop with a knuckle makes a distinctly "solid" sound near the edges, and a "hollow" sound anywhere else. With my desktop, there is NO WAY I'd be able to support 15Kg from the bottom of it. If yours is hollow anywhere, it won't either!

I also purchased a sit/stand desk leg setup from IKEA, but the top I purchased wasn't "officially" supposed to go with it. I was able to attach the legs to the wood in the top, but I've attached nothing in the center.

To accommodate the movement, I've got my tower CPU sitting on the floor next to the desk and long USB & video cables (10' IIRC - my CPU isn't right next to the desk) running to the desktop. Along the bottom edge of the desk, I installed some cup hooks along the edge into the solid wood for cable management, and I've got the cables run to the side of the desk where they drop down to the floor. When the desk is lowered to the sitting position, I've got a bit of a tangle of video cables, but I've got enough slack that I can raise it to a standing position without pulling on anything.

I looked long and hard to find a power strip with a long cord and with mounting slots on the back near the edge (not down the middle). I used the mounting slots to put it on screws at the edge of the desktop (into the solid wood), then all the monitors & other desktop accessories plug into the power strip with cords neatly bundled up under the desk. Then I've got the one power cord running to the ground where it plugs into the UPS. The cord is long enough to accommodate the vertical movement, as well.

At some point, I'll add another hook to hold the cables to the table bottom, then put a weight on each cable between the last two hooks. This will force the cables to be in a "droop" between these two hooks, yet allow it to slide as I raise the desktop. This should tidy up the rat's nest of cable while still allowing them to move. I just haven't been motivated enough to mess with it yet. :)

I agree with the other answers, most like, this will be fine, as long as you use the correct screws, pre-drill, etc. If you want to give this setup some extra support though, I would suggest you go get yourself a piece of plywood about that would cover the whole mounting area of the computer attachment, screws that are just short of the thickness of plywood+thickness of your desk, and some construction adhesive.

Lay a good bead of the construction adhesive on the back of the plywood and put it up under the desk, now screw in place with one screw, and then you can comfortably pre-drill the other spots and put some more screws in. Now you have a known, solid surface that is mounted pretty sturdily to the underside of your desk, and it will probably be easier to attach your computer to the plywood without so much risk of stripping holes in the particleboard.

I have nearly this exact set up, with a very similar computer tower mount and a 3/4" particle board desk top. It's very solid and has stood up to many knee bangings as well.

Be sure to use larger diameter screws w/ coarse threads. I used #10 x 3/4" pan head screws Though the screw length is the same as the particle board thickness they don't stick through because of the thickness of the metal mounting plate. 5/8" screws would be too short and may not hold as well.

You have some answers that are pretty off. That computer is heavy. No F'ing way you can screw that to the bottom of a moving desk.

But you can bolt it using a nut and cap. If you get exactly the right size you could predrill a space for your nut to sit below the surface at the top and then cover that.