Of course you can.
Night prayers are Mustahab and you can decrease the number of the zikrs as well as the number of the prayers itself, i.e. if you can't perform all the 11 Rak'ats at least pray the last three or even the last Rak'ah.
Many hadiths have emphasized the importance of the night prayer. In his will to Imam 'Ali (a), the Prophet (s) emphasized the importance of the night prayer three times. And in a different saying, the Prophet (s) addressed all Muslims by: "I recommend you to say the night prayer, even one rak'a, since it prevents one from committing sins, quenches God's anger and extinguishes the fire on the Dooms Day".
It is so important that it is recommended to perform its qada' if one fails to perform it in its valid time and the person who fails to perform it is considered as a loser. It is recommended that the night prayer be performed even when one is tired or on a travel. Some hadiths from Sunni sources imply that the night prayer used to be obligatory in the early days of Islam, but it became recommended later.
According to the words of the Infallibles (a), committing sins and overeating cause one to lose his or her occasion to say the night prayers.
For more info see https://en.wikishia.net/view/Night_Prayer