What type of engine does your TU1500 have? If the engine is an Iseki, it will have the model number on the side, something like E3AE1 or if a Mitsubishi, something like K3C. Unless someone has a TU1500 owners manual (not likely except in Japan), you are better off with an engine number, as many Iseki's share engine types. This will get you better info on valve clearances, etc. from forum members.
You would be safe to use UTF (Universal Tractor Fluid) for the transmission / rear end. Tractors that share the sump for hydraulics and gear boxes use UTF and Iseki's specify it for their tractors. There will be a dipstick or fill and drain plugs.
Front axles use SAE 80 and you simply fill until the axle is at least half covered.
Engine is fine with any good quality diesel 15-40 oil. It has to be diesel oil. Change out is typically 100 hours. If you live in a cold region of the country, 10-30 is fine for winter, as long as it's diesel oil.
The clutch end of some engines have a small gearbox. UTF is fine here, there is a fill and drain just like a standard transmission. Remove fill plug and add until it overflows.
There is no end to oil quality arguments, but I buy all my fluids at Wal-mart. I have diesels with over a million miles on Wal-mart oil, but I change out my oil like it's a religious edict and Wal-mart oil have served me well. If you have money to burn and think Wal-mart oil is substandard, then go for the gusto and buy Castrol or something that helps you sleep better at night.