Could they be planning to use them on Israel? Or could the Target be Turkey? A war with one of these nations would unify the Syrians behind the dictator. Its worth a gamble. What could a 105 MM cannon hit from Aleppo?
If the Syrians decide to have a war with Turkey. They would obviously begin by taking out the Patriot Batteries with Sarin Gas artillery. That would open a corridor they could lob Ballistic missiles through and onto Turkish Cities. Russian Armor is all set to go up in the former Georgia provinces. They certainly do not have to reinforce Iran now.
Anything within a 7 to 9 mile radius, limits depending on whether the projectile is rocket assisted (9 miles) or not (7.1 miles).
155 mm systems vary, but 30-40km (18.75-25 miles) is not unusual, and the Excalibur (ours) can do 50 km (31.25 miles) with the right ammo.