Since the world origin is a vector 3(0,0,0), the max limit that you can place an object would be 3.402823 × 10^38
since it is a floating point. However, as you are finding, this does not necessarily mean that placing something here will insure it works properly. Your limitation will be bound by what other performance factors your have in your game. If you need to have items placed at this point in the world space,consider building objects at runtime based on where the camera is. This will allow the performance to work at different points from the origin.
Unity suggests: not recommended to go any further than 100,000 units away from the center, the editor will warn you. If you notice in today's gaming world, many games move the world around the player rather than the player around the world.
To quote Dave Newson's site Read Here:
Floating Point Accuracy
Unity allows you to place objects anywhere
within the limitations of the float-based coordinate system. The
limitation for the X, Y and Z Position Transform is 7 significant
digits, with a decimal place anywhere within those 7 digits; in effect
you could place an object at 12345.67 or 12.34567, for just two
examples.
With this system, the further away from the origin (0.000000 -
absolute zero) you get, the more floating-point precision you lose.
For example, accepting that one unit (1u) equals one meter (1m), an
object at 1.234567 has a floating point accuracy to 6 decimal places
(a micrometer), while an object at 76543.21 can only have two decimal
places (a centimeter), and is thus less accurate.
The degradation of accuracy as you get further away from the origin
becomes an obvious problem when you want to work at a small scale. If
you wanted to move an object positioned at 765432.1 by 0.01 (one
centimeter), you wouldn't be able to as that level of accuracy doesn't
exist that far away from the origin.
This may not seem like a huge problem, but this issue of losing
floating point accuracy at greater distances is the reason you start
to see things like camera jitter and inaccurate physics when you stray
too far from the origin. Most games try to keep things reasonably
close to the origin to avoid these problems.