We have a seth thomas grandfather clock. we moved it, removed the weights, and pendulum, to redo the floor. We assembled it but now the pendulum works for 15 minutes and stops.?????

The clock must be levelled the same as when it was previously set up. In other words, if you didn't check the level of the clock before disassembly and reassembled it and re-levelled it, it may not operate because it might not be the same.
Some clocks have different weights for the clock, chime, and hour strike. Did you mark them and install them in the same location?
My Seth Thomas has a screw to adjust the swing of the pendulum to allow proper escapement on the gear, but you have to be able to determine which way the pendulum needs to swing more to make that adjustment. I may be able to help you with this!
You may need a clock repair service.
Let me know,
Gary

1, Wind the clock. If the pendulum still does not swing, check the hands of the clock. If the hands are touching each other, push the hour hand gently toward the clock face. If the hands still touch, gently bend the minute hand away from the clock face.

2. Examine the swing of the pendulum. If it moves, and then stops, or if it swings erratically, the clock is probably off-balance. Gently tilt the clock to one side and restart the pendulum.
Watch the swing of the pendulum. If it stops again or continues to swing erratically, try tilting the clock in the opposite direction. Tilt the clock at various angles, on each side, and front and back, until the pendulum runs smoothly and regularly.

Note the clock position in which the pendulum swings freely. Place a wedge underneath the clock in the place needed to maintain this angle. If a wedge alone will not hold the Seth Thomas grandfather clock in the proper position, try lifting the clock slightly up against the wall.

Use a screwdriver to attach a bracket to the wall at the appropriate position. Additional brackets may be needed depending on the angle required. It may also be necessary to employ a combination of wedges and brackets.