from datetime import datetime


def timestamp_seconds() -> str:
    """
    Return a timestamp in 15-char string format: {YYYYMMDD}'T'{HHMMSS}
    """
    now = str(datetime.now().isoformat(sep="T", timespec="seconds"))
    ts: str = ""
    for i in now:
        if i not in (" ", "-", ":"):
            ts += i
    return ts