15 and curtains fifteen cubits long are to be on the other side, with three posts and three bases.

Read Exodus 27:15 Using Other Translations

And on the other side shall be hangings fifteen cubits: their pillars three, and their sockets three.
On the other side the hangings shall be fifteen cubits, with their three pillars and three bases.
The curtain on the left side will also be 22 feet long, supported by three posts set into three bases.