It means the property stolen had a value between $1500 and $20000. This is a state jail felony punishable by between six months and two years in the state jail.
As noted this is the level of offense; you or someone you're asking on behalf of has been charged and possibly indicted for a State Jail Felony charge of theft of property with a value between $1,500 and $20,000. A SJF has a punishment range of 180 days to 2 years in state jail and an optional fine up to $10,000. More likely than not probation is an option but deferred adjudication is the best result so you can avoid a conviction. Some Dallas courts are reluctant to allow deferred based on prior criminal history but there are ways to move around the system.
You definitely want to avoid a conviction and need an attorney. Feel free to contact me to discuss your options in Dallas or the specifics of this charge.
Good luck