Is it considered usury or trade for a person to buy a plot of land for 20,0 dinars, possessing 15,0 dinars, then propose to a friend that he pay 5,0 dinars to become a partner in the land without registering his name in the deed, on the condition that he buys his share from him after two years with a 10% profit?

This contract is usurious and impermissible, because it is a loan with an increase, which is explicit usury. It also falls under the category of Bai' al-Wafa (a type of conditional sale) which is forbidden by Sharia (definition). The permissible scenario is to share in the land without stipulating its purchase, and with witnesses to the shared ownership.