HIT was already domestically producing a limited number (100?) of Turkish 155mm artillery pieces. So developing a 155mm gun doesnt make much sense unless there are 2 possibilities:
1) The 155m gun will be a light weight howitzers similar to the Chinese AH-4. Something which can be transported to strategic heights via the MI17.
https://en.wikipedia.org/wiki/Norinco_AH4_155mm_Howitzer#:~:text=The towed AH4 howitzer is,which allows greater tactical mobility.&text=Also, as a modern howitzer,km using rocket-assisted projectiles.
2) The 155mm Gun will be a self propelled artillery gun.
3) A combination of the 2. It would be make sense for Pakistan to create a 155mm self propelled gun turrent that can be used to upgrade that 1000+ tanks that are due for retirement. Pakistan could produce a limited number of towed pieces while created a universal 155m self propelled turrent platform that can be used to updated T59s, T69s, etc... in the army. Many countries are doing this for cost saving/logistics.
Pakistan already has 500+ self propelled guns mostly of american origin. If we can even convert 300-400 tanks to modern self propelled guns it would be a major boost to artillery brigades.
In the next few years we will induct 300 AK1s and 300 VT4s to the army. I could easily see 800 tanks due to retire.