ffmpeg - output file is twice as long as the input
Assuming that's the unabridged command, I do see many puzzling things.

-threads 0 is set here for decoding the input and is set to 0 = auto. Which is the default. Removed. 

-f lavfi is for supplying a filter-generated source, not for a set of image files. Removed.

-r 60 should normally be harmless here, but given the filter format and vsync later on, better to remove this confounding option.

-ar 48000 -acodec aac is for encoding audio, but no audio stream is supplied or generated, so inert here. Removed.

-shortest is needed when there are multiple streams being encoded, and you want the encoding to stop when the shortest stream ends, but there's only one stream, the image sequence, being encoded. Removed.

-strict experimental is needed if you are encoding audio using the internal AAC encoder AND your FFmpeg is older than Dec 2015. In any case, there's no audio encoding occurring. Removed.

-sn disables subtitles, but no subtitle streams are present. Removed.

-vsync 1 produces constant frame rate output but that's the default for MP4 output. Removed.

Use 

ffmpeg -y -framerate 60 -i image_seq.%06d.tif
       -preset medium -c:v libx265 -b:v 7340032 -pix_fmt yuv420p
       -movflags +faststart output_file.mp4