No problemo. I'm still a rookie myself. I've only been at it 18 months. I remember what it was like to just get my feet wet. I even had a DIY tray and arm assembly. It was butt-ugly but worked just fine. Keep in mind you're going to need a tray, arm and fiber optic cable with that 300. There's a YS27DX on Ebay, head only, for $329. BTW, from my experience, the fiber optic cable isn't an option with optical strobes, its a necessity. Sea&Sea has a way to stick it to the outside of your housing with some black velcro which you also use to black out your internal strobe (to avoid backscatter).
BTW, I haven't owned, or tried the SL960D but have heard others say nice things about it. I purchased my first Sea&sea strobe (YS27DX) a month ago and was impressed by how well thought out the connection of the fiber optic cable to a generic housing was. I was also impressed by the battery door which was the same as its high end strobes. I've already done a dive and was impressed by the lighting. So I'm happy with the Sea&Sea setup.
BTW, after a little research, the YS15 auto has no manual adjustment of the light output on the back of the strobe...its done automatically. I've read it struggles with macro. The YS25 will give you 6 manual power stops controlled by a dial on the back. So if the dollars are comparable, the 25, or 27 is what you want.