a person could probvably lift 50 to 60 kilos if the weight is compressed to small dimensions
a tank is awkeward, cos you have to balance it and it has different dynamics.
i have moved lots of tanks b efore, including 2x 1200litre 8footers.
and its nto easy. 15mm 6 foot tank is gonna be heafy.
The more people the better, 6 min to 8.
do it slowly, carefully but just lift fromt he knees.
your stand is key, how high is it?
if its low, thats easy, you can straighten arms and let the fingers anchor themselves in, if you have to lift it high tot he stand, thats where the difficulty starts.
good luck!