That doesn't sound right. The file size is what you'd expect, but the delay sounds wrong. The scratch space has to be reserved space and wouldn't be writen data if you are working such small files.
I doubt I'll know the answer, but whoeve can work out what is happening will need to know.
Are you using the 64 bit version of Photoshop? (If you are on a PC)
What are your settings in Preferences > Performance? A screen grab would be easiest.
Computer spec? Especially how much RAM
Looked for a way to edit my original post. If there is one I could not find it.
A bit of clarification (not sure it is needed) but when I say "allocationg" I mean the following scenario. PS is not started. I double click the 30MB file, PS starts up and I get a progress bar. It takes around 1 minute (sometimes more sometimes less) for this file to load.
While loading I refresh Windows Explorer and notice the size of the scratch disk temp file, slowly climbing to 40-60GB. The final size is not consistent. It jumps around within the mentioned range.
Windows 7 Pro, AMD FX-8320 3.5Ghz, 8 core, 8GB DD3 1600, a mid range 2GB Radeon HD7870, 126GB SSD as system drive and a 256GB SSD as scratch disk
64 bit version of PS Creative Cloud
I use 50% of memory (4GB) with "long and skinny" history keeping algorithm. Will post a screen grab shortly.
Edit: Around 10% of my files cause this kind problem to various degrees. Some are from over a year ago. I am thinking it must be something I am doing.