I had stopped playing for a while, but I'm coming back to this thread because I was experiencing the same issue after spinning off two Sims into a new household in an apartment. (At this point, I own everything but My First Pet.) Now, given that it was an apartment, space was limited. So it didn't have nearly the same number of objects, rooms, etc. It was significantly smaller.
And yet, I still experienced a guaranteed crash after going into Build Mode and then back into Live Mode unless I had just recently restarted the game. Load times were still excessive and I was still experiencing frequent crashes when trying to load the gallery, even if I had just restarted the game. I would rarely experience crashes from traveling, however. That kind of crash seems specific to a lot with too many items on it.
Now, before I went through the work of setting up a new save, I deleted and redownloaded the game and DLC, rebuilt my PS4 database (which has made the system menu snappier, so no regrets) and restored licenses. I still got crashes, but I was kind of expecting it.
So, taking the advice of PoptartJuniper, I created a whole new save. Before doing so, I saved my three played households and my personal custom builds. I also managed to save inventory items by placing them in the rooms/lots that I saved to my gallery (such as paintings, unfinished collection items, plants, etc). I then loaded them all into the new world.
Poptart was correct about aspirations/skills/etc being saved. Funds can also be recovered so long as you load the household in a specific way (click a lot, then click 'create new household to move in,' then place the saved household from your gallery while in CAS). If you do it any other way, you just get the default starting funds.
I even managed to re-create familial relationships by ordering my placements. When placing households with familial relationships, place the 1st generation, then add the second to the same household and edit the relationships while still in CAS. You can then spin-off the 2nd generation and add the third generation in CAS. (I had an unusually complicated family - the primary Sims included Bella Goth, who had an ex-husband and two kids in my old world. She married my Sim, then had four more kids, two who were in their own household. Meanwhile, the Sim she married had a daughter who'd married Bella's son and had kids of their own. But I still managed to re-create the familial relationships in CAS, though I had to upload and place an edited version of the Goth family.)
Basically, as long as the Sims you are importing are not in the generation previous to your already placed Sim, you can edit the family relationship without cheats (you can add a son, but not a father; a grandson, but not a grandmother). Of course, cheats would make the whole thing easier.
After all this, my game is loading faster (though I've yet to place all the lots that were in my old world, filling up empty spaces). It is also not crashing! So Poptart's solution works and, for the most part, can be done without losing much from your old world or using cheats.
Things that are lost: authorship of paintings (value also changes), physical graduation degrees and pictures (though the Sims keeps the degree accreditation in their traits), household/personal inventory that is not placed in the world, fish in tanks (must be placed individually in world), specific inventory items even if placed (mixed drinks become empty glasses), artifact quality from Salvadora defaults to poor, relationships to other Sims.
Retained: career/event unlocks, aspiration rewards, aspiration reward points, plant qualities, inventory items placed in the world, jobs/skills, fame, childhood traits (like Responsible), funds (if placed correctly as noted above), pictures taken by Sims.
(Also, somehow I saved the kids' Void Critters collection but I have no idea how since that should have been in their personal inventory. Also a candle from Eco Lifestyle that would have been in personal inventory, too. It even retained authorship.)
TL;DR solution: Crashes when traveling from home lot may be due to too many items placed on the lot. Crashes when loading gallery and/or exiting build mode into live mode can be fixed by creating a new save and you can save most things by uploading households/lots to gallery.
