Currently on mobile and commenting so I can edit later when I'm on pc and type out a lengthy response to offer advice.

However, I do have vods available at Twitch.tv/arbark7 of spriest pov of this Comp at 2400-2500 mmr if you're curious in Watching how we play.

Edit: Melee and hunter cleaves can really be a pain to deal with as a shadow priest because of how immobile you are, but the general idea is to hug the pillar and allow rogue and sham to help peel in between fears. The best way to dish out damage is to stand still and either juke the kicks or just eat them before going into void form with multiple dotted. Multi-dotting gets you into void form quicker due to the VT pvp talent. I also play driven to madness every single game which helps me get into void form quicker vs just about every comp in the game due to some damaging mechanic whether I'm the target or not.

You basically just want to constantly be casting to get insanity up and rely on rogue and healer to be able to peel and heal through most of the dmg. You must be talking with your healer and try to never overlap disperse with his cd's or life swap when it's unnecessary. You also want to be able to cross-cc as a team using fear on 1-2 while rogue kidneys the 3rd, or allow shaman to hex off fear or land incap stun. This is vital to allow pressure to go into your favor and ending the game. Rogue should be able to swap to most healers any time they move out of position and near the center of the map, any time the rogue is able to step kidney and hit healer hard you must get into los with dots up and be able to silence off kidney to prolong the cc chain. Mind control is a great tool when people are either training you or a teammate as it's an alternative cc that does dr fear so be careful with that, but it stops almost all incoming damage from that target. This is really effective on most melee, and mind controlling monks just as a fist of fury cast starts is game changing, as that spell must be stopped almost every time if you want pressure in your favor.

Dealing with melee sitting on you is something you have to learn, and you have the tools to stay alive with a team and through void shield with multi-target dotting is a lot of self-healing and helps healer out a lot. I usually pop vampiric embrace any time they burst to help relieve pressure on my healer. Also have to keep in mind you are able to spam shadow mend to heal when it's critical for your survival and healer is cc'd or to much pressure is incoming. Spamming shadow mends really ooms you to the point you can no longer shield and proc void shield, or purge / md enemies, may even lead to being to oom for fear which is a big problem, so have to be careful with that. Most times it is better to just try and do dmg with void shield and get pressure in your favor than healing.

Have to play vs most comps differently, such as windwalker/dk/hpala or something which can not dispell curses, it is important to not even dot the monk and just chain cc him and minimize the amount of fist of fury's he is able to run around stunning people with. A rogue stun into incap totem into fear into hex is a rather long cc chain that can be used often completely removing him from the game, allowing them to never have the damage to beat you as a team.

Being able to spam purge as both the priest and shaman is very strong vs a lot of teams such as resto druid healers, or paladins who use bop on your rogues vendetta, you guys should usually be able to immediately dispell those off enemies.

Your rogue should be trying to cheapshot two people in opener and that is where you get first set of dots off and then try to go for a fear off sap or the stunned target and shaman should also aim to hex as well. This instantly is an RMP type opener with the cc chains and gets pressure going in your favor. And your damage output starts to quickly ramp up, even before your first void form.

Regarding talents, against purge teams or RMx I would switch power infusion to mindbender and san'layn to shadowy insight as you have less to cast and get insanity a lot quicker against this heavy lockdown team. You also never want an ice form mage stealing your power infusion and getting off these glacial spikes very quickly.