Over here on the West Coast (of the US, to be precise) it's Tuesday, meaning that it is patch day.
7.1.5 is one of the promised "in-between" patches for Legion. We're not getting any grand new content* but we are getting some major class tuning, the adjustment and addition of many legendaries, and a few additions to existing features.
First off, the Brawler's Guild is coming back. Sadly, our old invitations are no longer valid, but it looks as if you'll be able to get them from multiple sources, like Emissary Caches, final bosses of dungeons, and some elite outdoor guys in Shield's Rest (the island in NE Stormheim.)
The patch will also add Mists of Pandaria timewalkers to the rotation, including all six of the original-to-Mists dungeons. There's a new mount and some other new collectables to go with the event, with a vendor at the Timeless Isle. Blizzard has said that we won't see Warlords timewalkers until at least the next expansion, with an expected pattern of having timewalkers only be for two expansions ago or earlier.
The patch will also bring with it micro-holidays. You can think of these kind of like Talk Like a Pirate Day and Day of the Dead - they won't have the extravagant stuff like bosses or meta-achievements. Instead, these holidays are meant to just liven up the world a little and give people an opportunity to do fun little things on occasion.
*While it's not technically part of the patch (in fact, it was added to the game files at launch,) the Nighthold raid is opening up the week following 7.1.5. The Nighthold is the official tier 19 raid, with sets and everything. As usual, Normal and Heroic will open up immediately, while Mythic and the first LFR wing will open up a week later, with new LFR wings opening up gradually over the course of the next month or two.
The Nighthold has ten bosses, including notable figures like Tichondrius, Grand Magistrix Elisande, and Gul'dan.
As of the most recent Blizzcon, we know a little about the patches going forward in Legion. 7.2 will add world content to the Broken Shore (right now it's just an island full of boss-level demons) and of course the Tomb of Sargeras raid. I would expect this patch to arrive some time in either late Spring (likely very late spring if then) or in the summer. We also know that we'll be going to the Eredar (which includes the Draenei) homeworld, Argus, in 7.3. We can probably infer that Legion's final raid will be coming in either 7.3 or 7.4, though the latter patch has not been announced (it really depends on whether 7.3 is going to be the final patch of the expansion or if it will set up Argus for a raid that comes later.)