Did i understand correctly that SPE is a simulator of remote-control CTC system used in Poland?
SPE simulates the MOR-1 system which is local control system. But there are very similiar MOR-2zs and MOR-2lcsr systems which are used to control multiple stations and CTC.
In Italy, our remote control systems have less functions compared to the local systems where the DR is IN the station. Is it the same with SPE?
In Poland CTC systems must have all the functions of local control system, plus the additional ones allowing them to control multiple stations.
In reality, what kind of lines have this kind of control system? Very busy ones or normal ones? Is this system still installed or it's old now?
They can be used on both busy mainlines and some minor branchlines. Branchlines often use the hybrid relay-computer configuration or the economical MOR-3E variant, both of which have a bit less functions than the main MOR-3 system. These devices and systems are installed and used to this day. The newer examples being recently opened Warszawa Główna station.